FIELD OF THE INVENTION
The present invention relates to an apparatus for adjusting the height and/or the angular position of a strip associated with the screen belt of a paper producing system, which strip extends transversely to the direction of motion of the screen belt. The strip has a carriage which is displaceable along a guide rail that is fixed to the machine frame, by which means the height and/or the angular position of the strip is adjustable.
In a paper producing system, it is known to dispose a plurality of strips, offset from one another in the direction of motion of the screen belt, on the underside of that screen. The purpose of the strips is on the one hand to scrape off the water that escapes from the pulp and passes through the screen. On the other hand, the strips create an air compression on their front ends (in terms of the direction of motion of the screen belt), which induces turbulence in fibers of the pulp, which in turn changes the structure of the paper or improves the quality of the resultant paper.
It is also known to embody the screen belts in two layers, with the pulp located between the two screens, and to associate such strips with both the underside and the top of the two screens. To achieve the technical effects sought, the heights of the strips must be precisely adjustable. In this respect it may be advantageous if the at least one screen is guided in a slightly undulating path by means of the strips resting on it.
It is also known to dispose the strips in angular positions relative to the screen belt. The first strips, in terms of the direction of motion of the screen, rest flat on the screen. By comparison, the further strips located in the direction of motion of the screen (i.e. downstream strips) are disposed such that they form an acute angle with the screen, on the order of magnitude of up to 5.degree.. Because of the wedge-shaped gaps that form between the screen and the strips, a negative pressure is exerted on the pulp located on the screen or between two screens, and by means of this pressure water in the pulp is removed by suction. For the removal of the water by suction, vacuum boxes are also provided.
The technological requirements and the technological conditions depend on the type of papers that are being produced. It is thus a very important requirement that the height and the angular position of each of the strips can be adjusted precisely and in a simple manner, and that such adjustments can be changed easily.
An apparatus with which the angular positions of the strips can be adjusted at any time is known from the European patent publication EP-A2 539 027. That prior art apparatus has a guide rail fixed to the machine frame; it extends transversely to the direction of motion of the screen belt, and a carriage is displaceable along it. The carriage forms the support for a squeegee strip disposed on its top. To enable adjustment of the angular position of this strip, the guide rail is embodied with a plurality of longitudinally extending grooves in its longitudinal direction, which grooves are engaged by bolts that protrude from the carriage or from the support for the strip. Since these guide grooves extend at an incline to the direction of motion of the carriage, and since the grooves provided on different sides are inclined differently, a displacement of the carriage relative to the guide rail changes its angular position, and as a result the angular position of the top of the strip facing the screen belt is changed as well.
However, the prior art apparatus is disadvantageous in the sense that the length of the strip must be equal to the width of the screen belt plus the length of the guide grooves. Taking into account the fact that such strips are manufactured from a high-quality ceramic material, this involves major expense. Moreover, protecting the various components from the intrusion of the stripped-off water presents difficulties in the prior art apparatus. Sealing strips have been provided for that purpose, but they are only partly effective.
Another device of this type is known from German published, non-prosecuted patent application DE 40 19 921 A1. The device is embodied with a strip associated with the screen belt, the strip being pivotally supported on one side and on the other having a wedge strip associated with it that is displaceable transversely to the screen belt. Displacement of the wedge strip enables adjustment of the angular position of the strip relative to the screen belt, without having to displace the strip itself.
However, that prior art device does not quite meet the requirements, because the strip can be adjusted only in its angular position, while conversely its adjustment in height is not possible.